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clarkema/State closures

Created March 6, 2016 14:54
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State closures
;; Lisp
(defun counter ()
(let ((i 0))
(lambda () (incf i))))
(setf indexer (counter))
(funcall indexer) => 1
(funcall indexer) => 2
(funcall indexer) => 3
# Perl
sub counter {
my $i = 0;
return sub {++$i};
}
my $indexer = counter();
print $indexer->(); # 1
print $indexer->(); # 2
print $indexer->(); # 3
@clarkema
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clarkema commented Mar 6, 2016 

(defun make-check (name)
       (lambda (x) (equal name x)))

(setf (symbol-function 'check-paul) (make-check "Paul"))

(check-paul "Bob") => nil 

(check-paul "Paul") => t

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